1. Field of the Invention
The present invention relates to a semiconductor through-electrode forming method for forming an electrode path from the front surface to the rear surface of a semiconductor IC.
2. Description of the Related Art
In a semiconductor IC in which an semiconductor element is formed on the front surface of a substrate, the electrical connection from an electrode of the semiconductor element to an electrode pad which forms an external electrode on the rear surface of the substrate may be made via a through-electrode which is formed by filling a conductive resin into a through hole formed in the substrate.
Conventionally, in order to form a through-electrode, a hole passing through the substrate, such as a silicon substrate, is formed, the side faces of the hole are insulated, and the hole is then filled with a conductive material.
Furthermore, currently, there is an increasing number of through-electrode structures in which, as a method for extracting electrodes to the rear surface after completing the semiconductor element, conductive paths are formed by passing through the silicon base material only, while leaving a thin electrode film on the rear surface side which is opposite to the surface where the semiconductor element is formed.
FIG. 7 is a cross-sectional diagram showing a conventional through-electrode composition.
In FIG. 7, numeral 1 denotes a substrate, 2 denotes a through hole, 3 denotes a conductor layer to which a binder has been added, and 4 denotes a conductor layer which does not include a binder.
In forming a conventional through-electrode, firstly, a through hole 2 is formed between the front surface of the substrate 1 on which the semiconductor element (not illustrated) is formed and the rear surface of the substrate 1 on which the electrode pad (not illustrated) constituting the external electrode is formed. Thereupon, a conductor layer 3 having an added binder is formed on the side walls of the through hole 2, and a conductor layer 4 which does not contain a binder is formed in the interior space which is surrounded by the conductor layer 3 with added binder, thereby forming a through-electrode. Finally, the electrode of the semiconductor element (not illustrated) and the electrode pad (not illustrated) are electrically connected by means of the through-electrode.
However, in the conventional composition, a conductor layer or resin is formed following the through hole, and a concavo-convex shape of indentations and projections is not formed in the conductor layer or the front surface of the resin. Therefore, the contact surface area of the interface between the inner surface of the through hole and the conductor layer or resin becomes small, and if an external stress, such as a thermal cycle, occurs, then the adhesiveness at the interface declines, and as a result, detachment occurs at the interface between the through hole and the filing material, cracks and fractures appear in the material, and there is a danger that connection defects will ensue. Furthermore, moisture infiltrates into the interface between the through hole and the filling material, an ion component is left in the device due to immersion in liquid, and hence there is a risk of leak defects due to corrosion.
Moreover, conventional compositions are based on the premise that the hole passes through the substrate, and in the case of a structure where a thin electrode film, such as an electrode pad, is to be formed in the bottom portion of the through hole, air bubbles are left in the bottom portion of the through hole and there is a risk that conductivity cannot be guaranteed satisfactorily.
Moreover, if conductive material is filled into through holes by printing, then due to the incorporation of air in the rolling of the printing material, air bubbles are left between the side walls of the through holes and the filling material, and there is a risk that water, or the like, will infiltrate, giving rise to corrosion of the metal or a decline in insulating properties due to the ion components contained in the water. Moreover, since the amount of filled material varies with the printing pressure, then the filling amount is non-uniform, and there is a risk that the thickness of the insulating material will become small, giving rise to insulation failures.
Moreover, if the filling material is supplied by squeegee, then insulating material and conductive material are left as residues on the surface of the substrate, and hence there is a risk of conduction problems.
Furthermore, if a conductor layer is formed by electroplating, then after forming an adhesive layer and seed layer which are necessary for forming a plating layer by sputtering or vapor deposition, an electroplating step is carried out by a wet process, and therefore the process is long, ion components are left in the device due to the immersion in liquid, and hence there is a risk of leak defects.
Furthermore, a conventional insulating film has a small film thickness, since the insulating layer is formed by a thin film forming process, such as CVD. Therefore if a current of 1A or higher is passed, a leak current may flow in portions where the insulating film has a small thickness due to variation in the thickness of the insulating film, thus giving rise to defects.
Moreover, since the process in conventional methods uses a large amount of indirect materials, such as photoresist masking, then time is required to switch between different machines, the defect rate is high due to the large amount of work input involved, and costs are also high.
Furthermore, in cases where the filling of the resin is carried out by an inkjet deposition method in order to resolve problems of this kind, if an inkjet deposition method is used to fill resin into a semiconductor IC having pad electrodes, on the semiconductor element forming surface side thereof, then the semiconductor element forming surface is open and exposed and therefore material projects onto or adheres to this semiconductor element forming surface, thus giving rise to problems such as conduction errors and insulating defects.